wind energy resource evaluation in a site of central italy ... - WindSim

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Turbulence is typical of industrial and atmospheric flows. Two different ways can bepursued with the goal of solving the turbulence problem for real flows using CFD.The first method numerically solves the Large Eddy Simulation (LES) equation, whilethe second uses the Reynolds Averaged Navier-Stokes equation.LES equation are deduced from Navier-Stokes Equation with a spatial averagingprocess. In this way only the large scale vortices are numerically solved, while thesmall scale turbulence Is “modelled”. LES simulation were introduced [7] to solve themesoscale atmospheric flow and today are also used for industrial flow, eventhough a very high computer power in terms of CPU and RAM is required.The most used way to solve real flows with a relatively low computer cost is solvingthe RANS equations. These equation, displayed in equations 1.5 and 1.6, are againdeduced from the N-S equation, but using a time averaging procedure instead. Inthis way all the turbulence is modeled and only the time averaged variables arefound with the simulations.Continuity equation1.5) =0Momentum equation1.6) ∙ = ∙ − − ∙ +In the RANS equations, terms that take account for turbulence appear. Arelationship between these terms and the time averaged variables is needed toclose and solve the system of RANS equations. Different turbulence models are usedto close the system of RANS equations, mainly based on the Boussinesquehypothesis [6]. An example is shown by equation1.7) − = ∙ + − + ∙ ∙7
1.5 The WindSim numerical codeWindSim is a CFD code used for evaluate the wind resources in a site by solving theRANS equations. It is produced by the company WindSim AS, Norway.WindSim uses a core constituted by the solver Phoenics (developed by Cham, UK),which solves the RANS equations with the finite volume method [11].WindSim contains a group of accessory software which help in the solution ofatmospheric flows.WindSim is constituted by 6 modules, which have to be run in sequence: the user isnot able to run the further module if the previous one hasn’t completed its work.The modules are listed below.1 Terrain2 Windfield3 Objects4 Results5 Wind Resources6 EnergyA brief description of each module is now reported, in order to analyze the maininput parameters and output results.1.5.1 TERRAINIn this module all informations regarding orography and roughness of the site ofinterest are inserted, through the file ***.gws . The ***.gws file is a characteristicWindSim format that can be created by the automatic conversion module, alsopresent in WindSim. In this way, WAsP files and ***.xyz files can be used to setterrain informations.The Terrain module also allows the user to define the parameters of the geometricalmodel, setting the grid discretization and the number of cells. Moreover, a lot ofother important settings needed for CFD simulations can be defined.8
Page 1 and 2: UNIVERSITÀ DEGLI STUDI DI CAGLIARI
Page 3 and 4: IndexIndex page IAcknowledgmentsVII
Page 5 and 6: CHAPTER 4: Characteristics of the s
Page 7 and 8: 6.7.1 Mean wind velocity page 1096.
Page 9 and 10: This thesis is the result of a prac
Page 11 and 12: WindSim is a software developed by
Page 13 and 14: CHAPTER 1. Atmospheric Boundary Lay
Page 15: Figure 1.1: Example of an atmospher
Page 19 and 20: (κ−ε RNG or the Low Reynolds),
Page 21 and 22: 1.5.4 RESULTSThe Results module all
Page 23 and 24: Figure 1.2: Example of TKE vertical
Page 25 and 26: CHAPTER 2. Simulations over flat te
Page 27 and 28: inlet position (0 meters), station
Page 29 and 30: 2.4 Height distribution factor sens
Page 31 and 32: e decreased, to avoid to build thin
Page 33 and 34: Figure 2.10: Vertical profiles for
Page 35 and 36: CHAPTER 3. Simulations over 2D hill
Page 37 and 38: Table 3.1: Measurement coordinatesS
Page 39 and 40: The results shown above demonstrate
Page 41 and 42: Figure 3.6: Sketch of the 15 km lon
Page 43 and 44: Figure 3.9: Influence of the height
Page 45 and 46: Figure 3.13: Zoom of the hill top r
Page 47 and 48: 3.5.2) = ∙.The two models for att
Page 49 and 50: H [m] hill heightν[m 2 /s] air cin
Page 51 and 52: Figure 3.18: Particular of the nume
Page 53 and 54: Finally, the horizontal x velocity
Page 55 and 56: Figure 3.25: Z velocity componentFi
Page 57 and 58: 3.6 RemarksA CFD study of a boundar
Page 59 and 60: Some experimental wind data of this
Page 61 and 62: Both the pictures 4.3 and 4.4 have
Page 63 and 64: Table 4.2: Description of the color
Page 65 and 66: In this periods, data are recorded
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In the following pages, a short des
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4.3.2 Mast 5424-15 m Period April-M
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4.3.4 Mast 5424-15 m Period Novembe
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4.3.6 Mast 5428-40 m Period April-M
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4.3.8 Mast 5428-50 m Period Novembe
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4.3.10 Mast 5428-30 m Period Novemb
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4.4.2 Mast 542870
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4.5.2 Mast 542872
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CHAPTER 5. Test of the Free Stream
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case the wind is blowing from the e
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Geometrical modelTable 5.3: Input p
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Figure 5.6: Vertical profiles in po
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The orthogonalization of the grid h
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Figure 5.9: Map of speed-ups for di
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Figure 5.30: Speed-2D at 30 m heigh
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Figure 5.12: Speed-2D at 30 m heigh
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CHAPTER 6. Analysis of the wind fie
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Table 6.2: Boundary conditions and
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6.5 Vertical profiles of VelocityTo
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characterized by high wind speed (5
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From the error analysis, it is foun
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Anyhow, the trend of the linear int
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Concerning the CFD simulations, val
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Analyzing RMS error table for tower
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A general overview of the figure 6.
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6.7 Cross Checking of wind dataIn t
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Figure 6.8 a/bFigure 6.8 c/dFigure
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Table 6.11: RMS error for cross che
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Figure 6.9 e/fFigure 6.9 g/hFigure
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Figure 6.10 g/hFigure 6.10 i/lFigur
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to have a better agreement during t
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Figure 7.2: Weibull fitting of the
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Figure 7.5: Perspective view of the
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The calculated AEP has been reporte
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ConclusionsIn this thesis the evalu
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Bibliography[1] CRASTO G. - Numeric
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